The Food and Drug Administration on Apr. 7 announced the approval of an extended-release form of gabapentin for moderate to severe restless legs syndrome.
The drug, known as Horizant (gabapentin enacarbil), is a prodrug of gabapentin. It was developed by XenoPort Inc. of Santa Clara, Calif., and GlaxoSmithKline.
"People with restless legs syndrome can experience considerable distress from their symptoms," said Dr. Russell Katz, director of the FDA’s Division of Neurology Products at the agency’s Center for Drug Evaluation and Research, in a statement. "Horizant provides significant help in treating these symptoms."
According to the National Institute of Neurological Disorders and Stroke, restless legs syndrome (RLS) is a neurologic disorder that is "characterized by unpleasant sensations in the legs and an uncontrollable, and sometimes overwhelming, urge to move them for relief." Mild to moderate cases are treated with lifestyle and behavioral changes. More severe cases warrant therapies such as dopaminergics, benzodiazepines, opioids, and anticonvulsants. Two other drugs were approved for the condition for moderate to severe RLS: Requip (ropinirole) in 2005 and Mirapex (pramipexole) in 2006.
The prevalence and incidence rates of RLS are currently not well known, according to the Restless Legs Syndrome Foundation. There is no cure and symptoms can worsen with age. The manufacturers estimate that 1%-3% of the U.S. population is symptomatic.
RLS remains underrecognized, "and many patients go untreated as a result," said Dr. Atul Pande, senior vice president at GlaxoSmithKline Neurosciences Medicine Development Center. "GSK has been committed to helping patients and healthcare professionals better understand and treat this condition. We are pleased to provide a new treatment" for moderate to severe primary RLS, he said in a statement.
XenoPort CEO Ronald W. Barrett said that Horizant was the "culmination of XenoPort’s efforts to develop a nondopaminergic therapy" for patients with RLS.
Horizant carries a number of risks and contraindications. Even at the once-daily dose of 600 mg, it can cause somnolence and "significant driving impairment," according to GSK and XenoPort. It is an antiepileptic, and that class of drugs has been shown to increase the risk of suicidal thoughts or behaviors. Horizant also increases this risk, and will carry such a warning, said the companies and the FDA. The dosage also needs to be adjusted for patients with renal impairment.